1. Field of the Invention
The present invention relates to storage devices including semiconductor elements. In particular, the present invention relates to storage devices to which data is written and from which data is read using selection transistors.
2. Description of the Related Art
A method for writing data to and reading data from a storage device including a semiconductor element with the use of selection transistors provided in memory cells is known. Typical examples of storage devices including selection transistors are dynamic random access memories (DRAMs) and static random access memories (SRAMs).
In the case of a storage device including a plurality of memory cells, a word line and a bit line are connected to selection transistors provided in the memory cells, and the memory cells can be selected or non-selected by a signal input to the word line.
Here, all the plurality of memory cells that are connected to one word line are transferred to a selected state when the word line is selected; thus, it is necessary to perform processing on the bit lines connected to all the plurality of memory cells. Consequently, as the number of memory cells (also referred to as the number of bits) increases, the cycle time required for random access increases. In order to solve such a problem, a method for dividing one word line with the use of a logic circuit has been devised (Patent Document 1). A method for dividing one word line with the use of a transistor has also been devised (Patent Document 2).